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The Cisco IOS software examines IP header options on every packet. It supports the IP header options Strict Source Route, Loose Source Route, Record Route, and Time Stamp, which are defined in RFC 791. If the software finds a packet with one of these options enabled, it performs the appropriate action. If it finds a packet with an invalid option, it sends an Internet Control Message Protocol (ICMP) parameter problem message to the source of the packet and discards the packet.
IP provides a provision known as source routing that allows the source IP host to specify a route through the IP network. Source routing is specified as an option in the IP header. If source routing is specified, the software forwards the packet according to the specified source route. IP source routing is employed when you want to force a packet to take a certain route through the network. The default is to perform source routing. IP source routing is rarely used for legitimate purposes in networks. Some older IP implementations do not process source-routed packets properly, and it may be possible to crash devices running these implementations by sending them datagrams with source routing options. Disable IP source routing whenever possible. Disabling IP source routing will cause a Cisco router to never forward an IP packet that carries a source routing option.

Nguyên nhân Disable chức năng trên

Routing and routing protocols can create several problems. The IP source routing, where an IP packet contains details of the path to its intended destination, is dangerous because according to RFC 1122 the destination host must respond along the same path. If an attacker was able to send a source routed packet into your network, then he would be able to intercept (chặn) the replies and fool (đánh lưà) your host into thinking it is communicating with a trusted host. I strongly recommend that you disable IP source routing to protect your server from this hole.